Radio control unit with interference suppression



July 3, 1945. c. D. HAlGlS 2,379,799

RADIO CONTROL UNIT WITH INTERFERENCE SUPPRESSION Original Filed Dad. 28,1939 2 Sheets-Sheet 1 CONTROL E' UN 11 HOOK DOW;

9/ T ANS. 95

CiDsHfiIGIS,

POWER LINE July 3, 1945. HA S 2,379,799

RADIO CONTROL UNIT WITH INTERFERENCE SUPPRESSION Original Filed Dec. 28,1959 2 Sheets-Sheet 2 AUDIO OUTPUT TO AUDIOSII'AGE FOR AUTOMATICBIASSILENCER Patented July e, 1945 UNITED RADIO KCONVTROLIUNITWITHINTER-FERENCE SUPPRESSION Carleton D. Haigis, ,Martinsville, N. J.

Original application Decemberj28, 1939, Serial No.

311,233. Divided and this application February 9, 1942, Serial No.430,131 i 14 claims. (c zso-zm This invention relates to radio signalingap paratus generally. More. particularly this inventionrelates to acontrol circuit adaptedjfor use in a radio receiver for controlling atrans-f mitter or other apparatus in accordance with y carrier Wavesthrough static and various forms of interference.

This applicationis a division of my application, Serial No. 311,233,filed December 28, 1939, I

for Two way radio communication systems, now Patent No. 2,292,222. i 1 IAn object of my invention is to provideya circuit arrangementadaptedtobe connected to one of the last stages or to thelast stage of asuperheterodyne receiver for the purpose of. de;

transmitter having two receivers which are interlocked so that thelfirstone receiving a signal selectively causes the transmitter to radiate. a

desirecljwave length, and Fig. .2shows a detailed circuit diagram of thereceivingcircuit of my invention including thecontrolunit.

The system which I provide: for separating interference from carrierforcontrol purposes 1 involves the balancing of its interference againstinterference, which balance is destroyed when the carrier is received. il Referring to the drawings in detail, and particularly to Fig. 1, whenreceiver 29 receives a veloping a controlpotential that variesinamplitude a fixed amount despite ,wide variations in amplitude of thereceived carrier.

Another object of this invention isto provide a circuit network thatresponds to weak carrier.

waves having low amplitude,:substantially the same in the presence of;a. large amount of noise;

only asmall] amount of) noise as it does when is present.

This invention is particularlyadapted for 1159.

in controlling the operation of a transmitter which may be a relaytransmitter at soIne.re-.-.- mote point. In order that the. transmitterat any station shall notube. put intooperation by static or byelectrical disturbances of a man-H.

made variety such asignition, commutatornoise 1 etc. nor by periodicvariations of these {types of disturbances, and shall becontrolledonlyby i the first receiver at the station that responds to acontinuous carrier wave, I utilize a novel circuit network to provide acontrol-potential that varies in amplitude a fixed amount despite.

wide variationsin amplitude of the said carrier wave and which respondsto weak carrier waves} or carrier waves having low amplitude substan-.

tially the same in the presence of a large amount of interference as itdoes when only a small.

amount is present.

Furthermore, the connections. are such that I l l the rate of change ofcontrol potential is a function of the amplitude of the incoming signal;being slower for a weak signal than for a strong one. H i

Other and further objectsand features of this invention will be apparentto thoseskilled in 1 the art to whichthisinventionrelates from thefollowing specification, claims and drawings. In

the drawings, Ibriefly,0Fig. 1 illustrates a sche I matic diagram of anapplication of the positive response control unit of my invention to arelay ceiver retains control of its selector relay 52 or message sentout on a channel A, to whichit is tuned, it provides at leads 42 acontrolrvoltage change as hereinafter described. The voltage,changeyapplied to control unit 40, shown. in de-- tail in Fig. 2,energizes the coil of relay 50, cans-- ing contacts 48' to close.Similarly, contacts 49 of relay 5|, are closed when afsignal is receivedby receiver 3| on asecond channel which will bereferred to as channel 0.The; coil of selector relay 52, isenergizedby'voltage from the sec-1T-ondary of transformer Sl when contacts 48 are closed. due toa signalbeing received on receiver 29, only when theselector switch I58 is setin auto position and only if relay 53 isnot energized and contacts 8|are closed; .Similarly,the "coil of selector relay 53 is energizedwhencontacts 49 are closed. by a signal in receiver 31, only if relay 52.has not been previously energized which would open contacts 58. Thus,it will be i seen that if relay 52 is already closedby asignal receiver29, it will remain so as long. as the,

signalpersists, even though a signal is received on receiver 3| duringthis period, because. even though contacts 49 close, the .coil of 53cannot be energized, since contacts 58 of relay 52 are ,open. At the endof the message, when receiver 29 no longer receivesthe signal,,contacts;Will open and relay 52 is de-energized.

similarly; when a. signal is received by re-.

' ceiver 3| on channel C, contacts 450i relay 5| close and energize thecoil of. selector relay 53,

provided relay 52 is not energized and its con-;

tacts 58 remain closed. By this means, a signal l in receiver 29 iscausedto energize relays 52 provided a signal in receiver 3| has notpreviously.

"energized relay 53. Conversely a signal accepted by receiver 3], willenergize relay 53provided a signal from. receiver 29 has not previouslyenergized} relay 52. By this means, either re- 53, even though a messageis received on-the when it is desirable to cause the station trans--mitter 33 to radiate on a different channel 13 when a signal is beingreceived on channelA to which receiver 29 is tuned, and to radiate onan- T other channel D when a signal is received on channel C to whichreceiver .3lviS. iullfld, Contacts 51 of relay 52 and contacts 8,6 ofrelay 53 are made to operate frequency changing relays within thetransmitter 33 thru leads 98 and 99.

' These frequency changes can be made by various wel kn n nset uch s bythe e r izin o a elay whoseccntacts act to dd a ac ty to the varioustunedcircuits and to connect afreq n ontrol uni u a a quartz c ta us thcon a ts 5 of ay Ella sig a on a receiver 29 will cause,. ransn1itter,33 to radiate on .a certain desiredlchannel, anda signal from receiver(31, thrucontactsfill of relay 5.3, will cause it s radi te, an a seconds le ted channe Furthermore, because of the interlocking ac: tionexplained above, control of the transmitter frequency cannot be obtainedby a signal coming into. one receiver as long as the other rei r s actie 11 he entra ta i n wh e the ransmit r i a sed to ra n sing channel wen either eive s ac t e frequency selectin (2011" tacts 57 of relay 5;and 8B of relay 53 are climb a d and he ystem. u t sns i same mannerexcept th t, the transmitter frequency, reains constant- 1 t The se ctorswit 5-8.. is pr vided sov that utomati controloi h t nsmitter y e re:

ceivs s 9 andfil ca be roken, in which case e, s-Qnta t o th swit h sthe 1? position.-

This preve o tass rom. rans mer fro a hin co ls of'relays 52am a conta t8" d o rela s & and 51- Sel ctor sw ch 51 oipsrmi smanua c oice of tansmitt ha k l so thatthe per tor at any tati an nd a messa e via micropone 5 and an mit e 3 on e h r chann y tracin the irsu t mthe secondaryof transformer 9| thruselector witc I58 when in os tion n nce' nta ts 3of tl1 Q kSW h $I nd thru. s t c s 8' i ela 5% t i l ound ha th @011 ofrelay 52 is energized, thus putting transmitter 'cradle and since theclosure of these contacts completes the. circuit from positions I and 2of them-anual selector switch. to relays Hand 53, the motion ofremovingthe microphone from its hook or cradle puts the transmitter on; theairson the channel selected; by switch I58.

121 c audio out ut: ro receivers 29 and 3.1 passesvialeadsfl i and 45thru. hook switch con,-v tacts 85 and sfi which are closed, when themicrothru volume controlling T-pads 81 and 88. The audio signal fromeach receiver is also applied to the transmitter thru the volumecontrolling pads 93 and 94 via leads 96 and 91 where they are am- 5plified and modulate the carrier wave of the transmitter, 7

Since the removal of microphone 55 from its cradle on hook switch 56opens contacts 85 and 86, the audio output from both receivers is dis-19 connected from transmitter 33 during the time that it is beingmodulated by the local microphone 55. Also the loudspeakers aredisconnected by-the opening of contacts 85 and 86 in order to eliminateoscillation which might be set up by 5 feedback and to eliminateannoyance to the opvcrater when he-is transmitting the message via micrphone 5;

control units 40 and 44 shown inFig. l in block diagram form areillustrated in detail in 20 Fig. 2, The anode of the diode portion ofthe initial combination diode-triode 6R7 tube 202 conveniently isconnected to one side of the last in-, termediate frequency transformer10 in the reive 0 31 (Fi bywayof a blocking con-s en er fipes zflsa lr athou h ot e -types. of tubes' y be used, I prefer for compactness to.utilize a c'ombination diode-triode, a second diode, and a finalamplifier connected in a rectifying ,and amplifyin arrangement to supplya potential change for control purposes when a carrier "is received,said connections, supplying substantially no potential change fromreceived interference. Thus I- pre fer to uti ze in this control unit 40a combination diorle-triodeilm of the 6R7 type, a double diode,

These type designations are in current commercial general use in theindustry. The anode of the diode portion. of the first combinationdiode-,

triodetuhe 2,!!2, the GRfLis connected conductively to the cathodethereof through two resistors 39- and. BL. thejunction P int. of whichis. connected through a capacitor Sitothegrid of the'triodeportion, Aresistor 63, connected at one end to the grid'of the triode portion ofthe tube 202 and at theothe'r end to a suitable source of negative 0potential, provides the proper grid bias for ampliefication. The primarywinding 64 of an output. transformer is, connected; to the anode of thetriode portion of" tube 2.02; 'The secondary wind-- ingBE of the outputtransformer is connected. by v '55 means of a potentiometer slider 66inseries with, a resistor 6'1; to a first one oi'the anode-cathode1paths of the double diode 6H6 tube 203, the other second anode and.cathode of which are inter-i connected through an output resistor 38which no constitutes part; of the input impedance, of the 61- '5 triode205 which acts as an amplifier and control tube, and is the final triodeof the control 3 unit. The latter tube is provided with anqoutputresistor 69 across which the control potential ing carrier as well as byreceived interference, is impressed upon and rectified by the diodeportion 70 Of b116 3? tube 202 and, unidirectional potentials. a

representative thereof appear acrosstheresistor 6 l adjacent he. c t deof the said diode P t L.

the remaining resistor 60. acting to complete a conductive path for theunidirectional current to.

phone isin its, cradle, toloudspeakersfia'and 90 the anode Receivedinterference, therefore,

ferenc'e; Superimposed onthis potential arethe audio components of theinterference. These components" are impressed upon the grid of thetriode portion of the tube through the'capacitor 62 connected to thejunction point between the two resistors60, 6|.

These components, therefore; are amplified by the triode portion andappear as potentials'across the primary winding 64 of theoutputtransformer, which has such characteristics that 'onlyinterference components abovea frequencyiwhich has a negligible amountof en ergy. from audio modulationiare impressed upon the next tube 203,

' the 6H6 double diode. Thistube' acting as arec- .tifier suppliesthrough its first diode portionuni directional potential across theresistor 61 con nected in series with it fromthe potentiometer 66 whichis in turn connected across the secondary winding 65 of the transformer.By adjusting the potentiometer 06, this unidirectional potential acrossresistor 0'! obtained by rectification ofthe selected interference abovethe cut-ofi frequency ofthe output transformerfmay be made equal to thatappearing across the resistorfi! directly connected to the cathode ofthe initial 6R7 tube 202.

It has been *found by experiment that the energy distribution ininterference of most types is spread over such a widefrequency spectrumthat the potentials appearing across theiload resistors 6! and 6'! ofthe SR? tube 202 and the 6H6 double diode 203 remain nearly alike inmag? nitude even though the interference level varies over a wide rangeof amplitudes. l

The potentials appearing'acrossthe said two resistors SI and 61 areapplied in series opposition 205 but permits. changes therein inresponse to.

to the gridof the SP5 control tube 205 thr0ugh a i time delaycircuitconsisting of a resistor connected to the grid of the 6F5controltube 205 and a capacitor 12 connected between its grid and 5relayshereinafter toioereferred to. i

cathode. The seconddiode sectionof the 6H6 double diode 203 is connectedacross the delay 1 resistor 08 and functions as will be further.

eXplained. w l. l

Innormal operation, with interference present adjusted at or near zeropotential by adjusting a is included: in theconnection'from the negativebutno carrier, the grid'of the 6F5 tube205 is terminal of the sourceofplate potential to 0 ground, and the slider filb of which is connectedto the cathode of the 6R? tube 202 and therefore to the grid of the SP5tube 205 through the series resistors 6|, 6?, 5.8, of'the diodes In suchevent;

the potentials across the output resistor fil of :the i diode portion ofthe GR? tube 202 and across ,the output resistor. 01 of the first;mentioned diode portion of tube 203 which is-connec ted to the secondary65 of the coupling'transformer; remain equal and opposite and cancelover wide variations of interference and do not materially aifect thepotentials of the grid of 6P5 tube 205. Under these conditions, spacecurrent flows. in the SP5 control tube 205, and unidirectional potentialappears across the outputresistor- 69 connected 'to the anode. Inpractice th outputresistor 59 has a magnitude of the order of 20,000ohms and the potential appearingacross =itx;is of the order of 10volts.- a i Changes in interference level have no effecton.

this output potential because of the balance of.

the potentials appearing across theoR'l. and. 61 -16 diodes or tubesi202and 203 H Whena carrier wave is received, ho wever, the

decreasesomewhat if the A. V. C. action. of th'e receiver reduces itssensitivity and, consequently, the amount of interference presentataudiofre quency. The lconstants of the circuits are so? chosenthat aweak signal with carrier impresses sufiicient negative voltage on thegrid of the6F5 tube 205 to completelyblock the said tube 205,

with consequentdisappearanceof'potential across the output resistor 69connected to the anode thereof. Because of the previously mentionedselective action of the coupling transformer 64,

65, audio modulation of the carrier, appearing across the diode loadresistor 6| connected tothe cathode of the6R7 tube 202;.has no effect onthe potential appearing across the output or load 1 resistor .61 ofthefirst portion of the 6H6 double diode 203 which isconnected between thesecondary 05,0f the transformer-and the cathode. of the first diodeportion ofthetube 203. 1 a

The terminalof theload resistor 61 from materially influencing thepotential-appearing across the output resistor. 60 of the 6515 tubeenable the operation of the transmitter In some instances it. isdesirable, particularly 1,: i when thereare several receiver-controlledtrans+ v mitters in one network which may automatically 1 relay signalsfrom mobile or fixed stations to one. central point, that the delay inactuating thew? transmitter be longer, the weakerthe signalw Forthatpurpose the grid of the 6F5 tube 205 is t lay-passed to the cathodethereof by tthelarge condenser 12 hereinabovereferred to, whichconde'nserreceives its charge through theresistorfid shunted by thesecond diode portion of the 6H6 Thegrid of the 6F5 tube 205 achieves ytive potential applied to .the saidresistor 08 only cordingly it doesnot effectively shunt the resistor I 1 w 68 "feedinglthe grid of tu be205, Whenpotential f'appliedfi When potential is removed betassejor; I

the cessation of a carrier signal, the said second I diode portion oftube 2.03 so rapidly conducts away i r i the charge acquired by theby-passc-ondenserfm that while time delay is provided uponttheapplication of a signaL'butlittle' or no delay results potential acrossthe output resistor 61. .lofflth diode portion of the GR? tube 202 isincreased, although the potential acrossthe: output resistor 61connected to the secondary of. thetransformer remains practically thesame, or may even u Fri in the cir-i cuitrof .the first diode. portionof tube203, connected-to thesecondary winding 65 ofthetransa former, iszconnected to the junction poillhbe ifl tween the output orloadresistors60, .6l,y.of the i f. diode portion of the tube 202 through anisolating. i resistor 2l0 having a resistance of the order of 500,000ohms, said resistor being for stabilizing purposes. The circuit thus fardescribed prevents received interference and variations of received.interference either of steady or transient type it when the signalceases. The primary purpose of havingadouble diode 203with this seconddiode portion across resistor 68-, instead of a single diodelike thefirstportion thereof, is to thus facilitate this delay action.

In actual use the potential appearing across the outputresistor 69 ofthe 6F5 tubeZtiis also uti- I lized'lto provide blocking grid bias forthe first audio freq-uency amplifier tube in the receiver itself when nocarrier frequency signal is-being received.

A- silent standby unafiected by interference or interference variationsand which maintains'substantially the full sensitivity of the receivereven with large amounts of interference present, is thus provided, andthe receiver is'quiet except when a, carrier .wave' is-being received.method of providing silentst'andby and control' potentials, offers greatadvantages in contrast to systems" in common use because of the abovedescribed interference neutralizing scheme. In silent standby systemsheretofore employed,

in the commontypes where the 6F5 tube 2'85 or similar tube is blocked byrectified intermediate frequency energy, interference as well as carrierblock the tube and the system must be adjusted so' that the maximuminterference which occurs at any location will not block .the' 6F5 tube205.

Under'tliese conditions, a 'ca'rriersignal of greater amplitudethanjth'e' maximum interference ever encountered, is necessary toprovide control and put thereceiver in operation. Thus in these priorsystems the enective sensitivity of the receiver is greatlyreduced,whereas in my system, the maximum'sensitivity-can be substantiallymaintained, a very desirable feature especially where it is usedto-receive mobile stations.

Asfh'ereinbefore mentioned; in my circuit, at

each station except the mobile stations, there are aplurality-of'receivers each of which is'adapted to control a singletransmitter for the purpose ofrelaying'an incoming message. To that endthe potential appearing acrossth'e output resistor 69 of the 6F5 tube2'05, is utilized. The said poten tial 'isapplied to the grid of onesection of a dual triod'e' 2060., 2061), such as the type BFBG, saidgrid beingc'onnected to the cathode of thesame tube by'way ofa'by-passcondenser F3. The constants of'the resistor M and the bY-Pass condenser13 are such that no appreciable time delay is introduced thereby and"the connecting resistor M is made sufficiently large to prevent shuntingof the out-' put're'sistor'69 of the 6F5tube 205. The capacitor 13connectedbetween the grid and the cathode of l the above controllingsection of the 6F8G tube 2060., 206b, is-used merely for stabilizingpurposes.

The potential on the grid of the controlling triode. section of the6F8G' tube 206a, 2061),

changes from its steady value of approximately 10 t voltsnegative toapproximately zero volts inde-' pendently of the strength of thereceived signal, because even a weak signal with carrier completelyblocks the grid of the 6E5 control tube 295. The "action of the networktherefore is of the on and Plate current-from this controlling orblocking section of the dual triode 2116a,- 206b, increases from zero to110.01 15 milliainperes when asignah is received, and reliable ruggedrelays can be used, thuseliminating the uncertainity attend-ant upon Irelays of the more sensitive types that are usually usedin similar,situations.

Because the entire network connected to the relay is above groundpotential by reason of the fact that. the lower terminal of theoutputresistor 69 ofthe SP5 tube 205 isconnected to the positive terminal ofthe plate potential source,

rectifier substantially constant whether the ,con-

trolling section is drawing current or not. To; accomplish this, aresistor 16 is connected be tween the common cathode terminal of the6F8G dual triode 2060,, 2 06b, and the grid of the second triodesection-of this tube, through which resistor 16 the curren-tsupplied bythe separate rectifier returns: to thesaid common cathode. When thecurrent through the controlling or blocking section'of the dual triode206a, 2861], is high, the grid of the regulating sectionbecomesmorenegative, thus reducing the current through Conversely, when the currentin thecontrolling section is reduced to said regulating triode.

zero by an incoming signal, the grid of the regulating section becomesless negative, and more plate current flows in said regulating section;Thus the potential fromztherectifier. source, applied to the blocking orcontrolling section of the SFBG dual triode 206a, 206b, can be keptsubstantially constant whether current flows through this section ornot. v

v The action of the system, therefore, is to provide approximatelyuniform current through the relay I50; when in the on condition, andsubstantially constant voltage from the separate rectifier. V

The relay I50; of course, may'be'provided with 'as many contacts as aredesirable for the pur pose of changing the transmitter from the standbycondition to the active condition, as

well asfor the purpose of changing the 'trans-- mitter frequencyby'actuatingother relays which in turn change the tuning of the variouscircuits an select the desired crystal.

However, in thepreferred arrangement, I use a single pair of contacts onthe controlling-,re- .lay I50 in the plate circuit of the 6F8G doubletriode 2060., 20611, to actuate other relays which perform the varioustuning and selective actions as illustrated inFig. 1.

Although I have shown merely a schematic of a portion of a police radiosystem constructed and arranged according to my invention and havedescribed certain specific features thereof;

offfitypaonetriodeof the 6F8G tube Z06a, 206b, 1

beingcompletely blocked as in the case of no signal,'or having zero gridpotential when a signal with; carrier is received.-

A relay winding I58 is included in the output element of thecontrollingor blocking triode section of the 6F8G tube 206a, 206b, which is devoid,of current when no signal is being received but which actuat'es itscontacts when a, carrier wave comes in and actuates a relay transmitter,corresponding to the action of relay 50 or relay 5| in thejarrarrgementof Fig. l.

it will be apparent to those skilled in the art that many modificationsmay be possible. My

invention, therefore, is not to be limited except insofar asisnecessitated by prior artand the spirit of the appended claims. I v

What I claim is as follows: 1. In a radio receiver, a thermionictub'e'hav ing input and outputcircuits, the input circuit comprising aresistor and capacitor network, the

output circuit being constituted by a resistor, a pair of'rectifierdevices for deriving two potentials each substantiallyproportional to received interference, connections for impressingthe ingand selecting a desiredportion of said re-.

, tive When no carrier is being received.

2,379,799 said potentials opposing. balanced relation across said inputcircuit to provide substantially ,zero grid potential: independent ofinterferencelevel, and means connected to one of said rectiif fierdevices for controlling the potential derived therefrom tojimpress :ablocking potential across said'inputcircuit uponreception of acarrierwave.

a 2. In aradio receiver, an auxiliary thermionic system which issubstantially without effect on the normal receiver characteristics innormal reception, said auxiliary system comprising a first 'rectifyingdevice which is adapted to rectify any part of the energy received,means for amplifyceived energy of determined frequency char- ,of saidthermionic amplifying tube, saidrectifying devices and connections beingso adjusted ,thatlthe output of said rectifying devices provides on saidinput circuit of said amplifying tubesubstantially zero potential withno carrier signal applied and Without response to interference beingreceived, and further provides a blocking potentialacross said inputcircuit of 1 said tube upon reception of a carrier wave. 3. In acarrier-signal-responsive,interference non-responsive, control unit foraudio receiver, l

meansvfor deriving a portion of the signal trav- =ersing said receiverincluding carrier components l and interference components, firstrectifying interval whose length is an inverse function of the istrength of said carrier signal. a

W6. A controlunit according to claim f3, and an output circuitcontrolling arrangement connected 1 to the output circuit ofsaidcontroltube andhavingloutputterminals to which energy is selectivelyapplied according to whether voltage is applied to the output circuit ofsaid control tube, said circuit controlling arrangement comprising meansformaintaining constant the output voltage of said circuit controllingarrangement under variousconditionsof operation.

,7; In a radioJreceivenuan auxiliary thermionic Q amplifying tube havinginput and output circuits,

acteristics a secondrectifying device adaptedj t to rectify said desiredportion, a thermionic amplifying-tubehaving an input circuit and an out-;put control circuit, and connectionsfor impress-c ing in opposedrelationship, the output of-both said rectifying devices across theinput circuit said input circuit comprising a. conducting i path to theggrid of, said tube, said outputflcircuit comprising an impedance,element, means comprising circuit elements and "frequencydiscriminatingmeans and a pair of individual rectifying wmeans connectedforderivinglfrom the main signal channel of said receiver two potentialseach substantially proportional to received interference, connectingmeans connected for impressing said derived potentials in opposingbalanced re- 25 lation across said input circuit to provide thereacrosssubstantially zero grid :biasingpotential duejto interferenceindependent of, the inter ference, level, output control meanswhichblocks ,yWnen a certain potential isapphedtnereto; and

means comprising an output impedance element 1 l for rectifying saidderived portion, amplifying means for amplifying the so rectified,derived portion, frequency selective means for trans-u ferring said sorectified derived portion, and

, adaptedto suppress audio frequencies, adjustable voltage ,dividermeans connected for ,adjustably delivering a desired portion of thevoltage outputof said transferring means, second rectifying meanscomprising an output impedance element connected for rectifying thevoltage so delivered by said adjustable voltage divider means, a control tube having an input circuit and an, output circuit, and aconnection to theyinput circuit t of said control tube comprising saidoutput inipedance elements of said first and second rectify- ,Said inputcircuit comp control circuit means connected to said output circuit andconnected to impress a blocking potential upon saidoutput control meanswhenno carrier frequency signai energy is received oy said t receiver, Iand to remove sald locinng potential when carrier frequency signalnergyis received.

8. In a radiorreceiver an auxiliary thermionic amplifying tube havinginput and output circuits, rising a conducting path to the grid: of saidtube, said output circuit comprising an impedanceelemendmeans comprisingcircuit elementsand freq'uency discriminating a means and a pair ofindividual rectifyingmeans connected for deriving from the main signal rchannel of said-receiver 'twopotentials each substantially proportionalto receivedinterference, 1 connecting means connected for impressingsaid derived potentials in opposing balanced relation across saidinput-circuit to provide thereacrosjs output: control means which blocksing means, said output impedance elements being connected serially insaid connection and being pOle'dto oppose each other, wherebysaidvoltage divider means may be adjustedwhen interfer fence withoutcarrier is received so; that substanftiajlly novoltage is then appliedto the input circuit of said control tube.

, 4. A controlunit according to claim 3, an acg connection from theoutput circuit. of said con- "trol tube to anelectronio element in themain signal path of saidfreceiver on theoutputside thereof with respectto the point of deriving said derivedportion, said control unit and saidconnection and said electronic element being arineffecranged to rendersaid electronic element 5. A control unit according to claim 3, theconanection from said input circuit of saidcontrol tube to said outputimpedance elementof said second rectifying 1 means comprising electricaltime delay means adapted to delay the application of energy to the inputcircuit ofsaid control tube when a carrier signal is received for ansubstantially ZBIO', grid biasing potential due, tointerferenceindependent of the interference level,

' EQwInaJradi receivercomprising'an audiofrequency portion, an auxiliarythermionicamplifying tube having input and output circuits, said inputcircuitcomprising a conducting path to the grid of said'tub said outputcircuit cornprising an impedance element, mean comprising c1rcu1telements and frequency discriminating means anda pair of individualrectifying means connected for deriving from the main signal channel ofsaid receiver two potentials each substantially proportional to receivedinterference,

connecting means connected for impressing said derived potentials inopposing balanced :relation ut circuit and potential upon I no carrier,fre- Jquency signal energy is received by saidreceiver,

across said input circuit. to. provider .thereacross substantially zero.grid biasing potential'due to interference independent oftheinterferencelevel,

and control circuit means connected toisaid output circuit andconnected. to impress aiblocking potential across said audio-frequency;portion 1Q.., In a radio receiver having .an audio-frequency portion, anauxiliary thermionic "amplifying. tube having input and outputcircui'ts,said in- ..put. circuit comprising a conducting path to the grid of saidtube, said output. circuit comprising a resistor, means including a pairof rectifying I devices for deriving from the main signal channel of.said receiver. two potentials each substantially proportional toreceived interference,-- connecting means connected for impressing saidderived po-= tentials in opposing balanced relation acrosssaid inputcircuit to provide thereacrossisubstantially, zero grid potential due.to interference independentof the interference. level, said outputcircuit. comprising means formaintaininga block-; ing potential acrosssaid resistor when no carrier frequency signalenergy. is being. receivedbyssaid receiver, and connections between saicl resistor and saidaudio-frequency portion for applying said blocking potential tosaidaudio-.frequency portion when no. carrier frequencysignal. energy isbeing received. .i

11, In. a radio receiver having an audio-frequency amplifying portion, athermionic tube having. input and output circuits, theinput circuit;comprising a resistor and capacitor networlgthe output circuit beingconstituted. by a, resistor, a pair of rectifier devices for derivingtwopotentials each substantially proportionalutoreceivedinterference,connections for impressing the said po-.-

tentials in opposing balanced relation across said. input circuit,.meansconnected. to one of said rectifier devices for controlling thepotential derived therefrom to, provide across saidtinputicircuitsubstantially zero potentialrindependentof.

interference, level to impress a; blocking potential a ross said inputcircuit :upon reception; of a car- 71 .1; wa e, nd. onnections forsupplying. ablocking potential from. said; output resistor to theaudio-frequency amplifying. portion .of the receiver during such times,-as acarrier waveiis; not

' beingreceived, whereby theeondition. known as silent standby isachieved irrespective.ofareceived interference without resort to.fixed;.reduction of the sensitivity of the receiver. .N

non-responsive, control unit for ,a radio. receiver,

means for deriving a portion of the total. received signal energytraversing said receiver including carrier componentsand interferencecomponents, H first rectifyingmeans comprising anoutput impedanceelement for rectifying said derived portion, frequency selective meansforutransferring said so. rectified derived portion. and adaptedtosuppress audio frequencies, adjustable transducer means connected foradjus'tably. selecting a desired portion of thevoltage output of said:transferring means, second rectifying means. comprising- .an outputimpedance. elementconhected for rectifying the, voltage so, selected by;said adjustmay be adjusted when interferencelwithoutcarrier is receivedso that-substantially .no volta ge is then applied tov the input circuitof saidcontrol tube. I I 13. Ina radio receiver, an auxiliary thermionicamplifying tube having input and. output circuits,

said input circuit comprising a conducting path I to the grid of saidtube, said output circuit comprising an impedance element, means;comprising circuit elements and frequency discriminating means and apair of individual'rectifyingmeans connected for derivingfrom the mainsignal: channel of said receiver two uni-directional potentials eachsubstantially proportional to-received-interference, connecting meansconnected for impressing said derived unidirectional potentialsinopposing balanced relation across said inputcircuit toprovidethereacross substantially zero grid biasing potential due tointerference independent of the interference level, output control meanswhich i i 55 12 Ina carrier.-signal responsive,1 terferenca blocks whena certainpotential is applied thereto, and control circuit meansconnected to saidoutput circuit and connected to impress a blockingpotential upon said outputcontrol means when I no carrier-frequencysignal energy is received by said receiver, and toremove said blockingpoten: tial when carrier-frequency signal energy is received. I l

I 14. In a radio receiver system, a first auxiliary rectifier deviceconnected to an intermediate stage of said receiver, a first resistancedevice con- 5 nected across said first rectifier device, an aux-. 4 2

iliary electron amplifying device having input and output circuits,saidinput circuit beingconnected across said first resistance device, afrequency discriminating device connected; to said output circuit, asecond rectifying device cannected'to said frequency discriminatingdevicega second resistance device connected; to said" second rectifyingdevice, said first and second resistance devices being connected inoppcsedrela- 'tionship, said receiver comprising a. controlled outputunit which is connected to be controlled by thecombined potential acrosssaid first and second resistance devices, whereby the combined potentialacross said first and second. resistance devices which controls saidoutput unit istsubstantially zero in the absence of a carrier waveCARL-ETON n. .niucrs;

